This invention relates generally to gas turbine engines and more particularly to gas turbine engine components formed in part from high temperature foil materials.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In a turbofan engine, which typically includes a fan placed at the front of the core engine, a high pressure turbine powers the compressor of the core engine. A low pressure turbine is disposed downstream from the high pressure turbine for powering the fan. Each turbine stage commonly includes a stationary turbine nozzle followed in turn by a turbine rotor.
Gas turbine engine hot section components, in particular the combustor and high pressure turbine section components, operate at extremely high temperatures and need to be cooled to have acceptable longevity. Cooling is typically provided by extracting relatively cool air from an upstream location of the engine and routing the cooling air to components where it is needed. Conventionally the components to be cooled are hollow and have provisions for receiving and distributing the cooling air by various methods, for example the components may be film cooled by providing a plurality of passages which eject a blanket of cooling air over the surface of the component, or the components may be convectively cooled by causing the cooling air to flow through various internal passages.
Because the rate of heat transfer from a component is proportional to the wetted area (i.e. the surface area exposed to cooling flow), known methods of improving heat transfer include various ways of increasing the wetted area.
Rough elements, such as dimples, cavities or short pins, have been commonly used in many designs to enhance the wetted surface area. The enhancement is quantified by the ratio of the increased surface area to the original surface area, A/Ao. These elements are often incorporated in cast components. Therefore, the size of the features and the surface area enhancement are limited by the capabilities of the casting process. The enhancement A/Ao with cast features is normally less than about 2.0. Other surface area enhancement techniques are known, such as the application of particles to a mold to create cavities in the as-cast surface of a part, or weld build-up to create miniature surface elements, e.g. small diameter hemispheres. The surface area enhancement ratio of these techniques is typically not much greater than about 2.5.
Accordingly, there is a need for a technique that can increase the wetted surface area of a component exposed to high temperature operation to a greater degree than previous methods.
The above-mentioned need is met by the present invention, which provides a wall structure for a gas turbine engine component which comprises a wall having a first side facing a flow of hot gases and a second side exposed to a source of cooling fluid. The wall has a plurality of holes formed therethrough, and an outer layer disposed on the first side. The holes greatly increase the wetted surface area of the wall exposed to cooling flow.